d d

1
4. Alcohols from ketones and aldehydes
d -d

• sp2
• trigonal planar (1200)
• strongly polarized double bond

Reactivity?
addition
nucleophilic
2
Nucleophilic Addition

• Change of hybridation
• Adding complexity to the molecular structure
• Converting a carbonyl to alcohol

3
Aldehyde
alcohol H2 LiAlH4 NaBH4
Cr2O72- MnO4- OsO4 Ce4
4
However
No contribution
(1)
(-1)
(-1)
No contribution
(1)
(-2)
(1)
(1)
2 el
-2 el
5
5 x 2 x
R-CH2-OH R-C(O)H
2 el
MnO4- 5 el Mn2
5 RCH2OH 5 RC(O)H
10 el 2 MnO4- 10 el
2 Mn2
2 MnO4- 5 RCH2OH 2
Mn2 5 RC(O)H
2 MnO4- 5 RCH2OH 2
Mn2 5 RC(O)H 8 H2O
2 MnO4- 5 RCH2OH 6 H
2 Mn2 5 RC(O)H 8 H2O
Balanced !!
6
From the qualitative point of view
Oxidation
Reduction Gaining O (increase ox
state) Loosing O (decrease ox
) Loosing H
Gaining H
RCH2OH RCH3
reduction RCH2OH
RC(O)OH oxidation
CO2 gt RCOX gt R2CO gt RC(O)H gt RCH2OH gt
RCH3
4 3 2 1

7
PCC
10 alcohol aldehyde
carboxylic
acid 20 alcohol
ketone
MnO4- basic condition
CrO42- in acid
A variety of selective oxidants
PCC pyridinium chlorochromate
8
Mechanism of oxidation
9
Mechanism of reduction
Ease of reduction
10
5. Using Organometallic compounds (Chemistry of
carbanions)
M Na, K Mg, Li
Pb, Sn, Hg, Tl
Versatile and useful
explosive
strong base (H-abstraction), strong nucleophiles
11
Preparation
R Br 2 Li R Li
LiBr
Ethers are the preferred solvents but
ethers are slowly attacked and decomposed